1. Field of the Invention
This invention relates generally to spinal fixation systems, and more particularly to a plate to immobilize the L5 vertebra with respect to the S1 vertebra.
2. Description of Prior Art
Various types of plating devices and systems, have been used to stabilize portions of the spine. For cases in which interbody fusion is desired in the lumbar-sacral region, stabilization using plating has been preferred by many surgeons for good fixation and to avoid damage to the vascular and nervous system components adjacent the anterior surfaces of the L5 vertebra. A plating system for stabilization of the L5-S1 junction is disclosed in U.S. Pat. No. 5,127,912 issued Jul. 7, 1992 to Ray and Ashman. It is a posterior system. While posterior fixation systems are often used in anterior/posterior fusions, the anterior surgical approach to the fusion is preferred from several perspectives. Less blood loss and reduced post-operative pain can be achieved. Also, effective anterior plating could avoid the additional posterior surgery necessary in the past to provide the additional stabilization needed to establish a reasonable fusion rate.
U.S. Pat. No. 6,045,552 issued Apr. 4, 2000 to Zucherman and Hsu discloses a plate for immobilizing the L5 vertebra with respect to the S1 vertebra. Earlier patents and publications are cited in that patent. Also, it is understood that Kostuick and Yuan had modified anterio-lateral plates, for example (e.g., the Syracuse I Plate) for use on the anterior lumbar spine. Also, it is understood that earlier literature reported clinical experience (Humphries and Hawk 1951, 1961) with an anterior lumbar plate manufactured by Austenal Company, New York. There remains a need for additional stability to an anterior lumbar interbody fusion using the same anterior surgical site for plating.
Described briefly according to the illustrated embodiment of the invention, a plate is provided having curvature in two planes such that it conforms to the curvature of the L5 vertebral body and the patient""s lordotic curve. Holes are provided receiving screws for anchorage in the vertebral body and sacrum. The screws and receiver holes in an upper portion of the plate are generally perpendicular to that portion of the plate. A lower portion of the plate is formed with a flange or foot portion which provides a wider base end area for support on the upper face of S1 in the L5-S1 interspace. The foot portion is also arranged for appropriate entry angle of screws into the sacrum such as to improve anchorage in the sacrum. The screws and receiver holes in the lower portion of the plate are through the front and bottom walls of the lower portion of the plate and at a steep angle relative to the front of the plate and engaged with the cortical bone of the sacrum at the superior end plate and at the S1-S2 junction. The foot portion also incorporates anti-backout and low profile features. The anterior lumbar plate is situated to maintain the anterior interbody bone graft in compression by resisting tensile forces during extension. The plate can also be extended to the L4-L5 junction by increasing the length of the plate and inclusion of holes in the upper portion for anchoring to L4.